Revert "Removed IncrementValue and DecrementValue event."
Revert "Removed IncrementValue and DecrementValue event."

This reverts commit 5b4e2a05398df66f024be7f455b09989659c0940.

batzen/MahApps.Metro,jumulr/MahApps.Metro,ye4241/MahApps.Metro,MahApps/MahApps.Metro,Danghor/MahApps.Metro,xxMUROxx/MahApps.Metro,pfattisc/MahApps.Metro,psinl/MahApps.Metro,Jack109/MahApps.Metro,chuuddo/MahApps.Metro,p76984275/MahApps.Metro,Evangelink/MahApps.Metro